Two-stroke engines



June 13, 1961 A. BRUEDER TWO-STROKE. ENGINES 3 Sheets-Sheet 1 Filed Nov. 28, 1956 q it! wa t!! Mme/Var Amo/ne Brueder By his affameys June 13, 1961 A. BRUEDER 2,988,070

TWO-STROKE ENGINES Filed Nov. 28, 1956 5 Sheets-Sheet 2 mmswfar A 0/0/06 5/06 der By his af/ameys June 13, 1961 A. BRUEDER 2,988,070

TWO-STROKE ENGINES Filed NOV. 28, 1956 3 Sheets-Sheet 3 An/a'ne Brueder By h/s a/fomeys filmmdw United States Patent 2,988,070 rwo-srnonn ENGINES Antoine Brueder, Paris, France, assignor to Societe Anonyme Andre Citroen, Paris, France, a French com.

This invention relates to two-stroke engines of the controlled-ignition type in which the ignition is fired, eg by means of a spark plug. It is well-known that in such type of engine the scavenging air ratio has to be varied in order to vary the power output; as a result difficulties occur in operation at low power.

One such difliculty arises from the fact that at the beginning of the scavenging period the pressure within the cylinder is greater than the scavenging pressure; this results in forcing burnt gases into the scavenging air circuit, the amounts thus discharged being quite small for high scavenging ratios but increasingly large as the scavenging air pressure is reduced.

This discharge interferes with the operation in two different ways; first there occurs in each cylinder a reciprocatory motion which disturbs the scavenging process, and moreover, in the case of multicylinder engines, a cylinder may interfere with the operation of another cylinder.

It is the object of this invention to provide an improvement in two-stroke engines which will greatly reduce the above-indicated drawbacks.

According to the invention, a variable obturator or flow-obstructing member is inserted in the scavenging air circuit ahead of the cylinders, this obstructing member being so connected with the scavenging air ratio adjusting means that the free flow section provided by the obturator member will be proportionately smaller as the rate of flow of the scavenging air itself is smaller.

This obturator member generates a pressure drop or loss of head which is higher in proportion as the cross section of the free flow passageway is smaller; the scavenging air pressure will therefore be higher, for a given rate of air delivery, than if the obturator were not provided. Furthermore, the flow section for the entry of burnt gases into the scavenging air circuit is likewise reduced. Both effects therefore contribute to a reduction in the discharge of burnt gases into the scavenging circuit.

From the statements just given it will be seen to be desirable that the obturator member be placed as close as possible to the scavenging port.

However, in the case of multicylinder engines, if it is simply desired to eliminate the objectionable effect created by an interaction between two cylinders, the variable obturator member may be positioned further on along a common line feeding the cylinders in which no mutual disturbing action is present, all the respective feed lines being connected with the general scavenging mixture or air intake manifold.

Embodiments of the invention are described hereinafter by way of example but not of limitation, with reference to the accompanying drawings wherein:

FIG. 1 is a diagrammatic view of a one-cylinder ens FIG. 2 is a diagrammatic view of a four-cylinder engine;

FIG. 3 is a view similar to FIG. 2 of a modified construction.

There is shown in FIG. 1 a cylinder 1 provided with an exhaust 2 and two intake passages 3. The latter are connected by way of conduits 4 with a common manifold conduit 5 which is connected with the outlet of a centrifugal compressor 6. Inserted in each of the conduits 4 is a butterfly valve 7, both valves being secured 2,988,070 Patented June 13, 1961 on a common shaft 8. Regulation of the valves 7 by' rotation of the shaft 8 simultaneously serves to adjust the discharge rate of the centrifugal compressor 6 and simultaneously to limit or increase flow into the intake passages 3, with the result that the free flow section area provided by the valves will be low in proportion as the discharge rate of compressor 6 itself is low.

Since two cylinders, whose action on the crankshaft is 180 apart, do not interfere with each other, a common obturator member may be provided for each pair of such cylinders. Thus, in the case of a conventional four-cylinder engine, there would be two obturator members. In FIGURE 2, the invention is shown as embodied in such an engine which has four cylinders 9a, 9b, 9c, 9d, the ignition sequence therein being 9a, 90,

. 9b, 9d. The cylinders 9a and 9b which according to universal or conventional arrangement act 180 apart in the cyclic sequence of cylinder action in engine operation are supplied with scavenging air by a. manifold 10a connected thereto by Way of the pipes 11. Similarly cylinders and 9d are fed with scavenging air by a manifold 10b connected therewith by Way of pipes 11. The pipes 10a and 10b are connected by Way of a conduit 12 with the outlet of a compressor 13 having a filter 14 inserted in its intake.

The conduit 12 further communicates with a return conduit 15 which delivers the excess air back to a point ahead of the compressor 13. Placed in each of the pipes 10a and 10b is a butterfly valve 16a or 16b secured on a common shaft 17 which further carries a third butterfly valve serving to regulate the connection between the conduits 12 and 15, the valve 16c being opened when valves 16a and 16b are closed and vice versa.

When the valve 16c is opened, a larger amount of the air discharged by compressor 13 is able to flow back to the compressor intake so that the rate of delivery of scavenging air from pipes 10a and 10b diminishes. At the same time however the valves 16a and 16b close down so that the net result is practically the same as that obtained in the example of FIG. 1, since the scavenging periods in cylinders 9a and 9b on the one hand and 9c and 9d on the other, do not overlap.

The embodiment of FIG. 3 is like FIG. 2 except that a butterfly valve is disposed in each of the conduits 11. The arrangement is therefore more complicated than in the embodiment of FIG. 2, but efficiency is improved since the burnt gases cannot here be forced into the pipes 10a and 10b as they could in the form of FIG. 2.

It will be understood that the invention is not limited to the forms of embodiment described and illustrated, but that it includes any modifications thereof.

What I claim is:

1. A multi-cylinder two-stroke internal combustion engine of the spark ignition type having inlet and exhaust ports for each cylinder and in which cylinders not having a common scavenging period are grouped, a supply conduit individual to each group of cylinders, a compressor supplying scavenging air to said cylinders through the conduit to each group, butterfly valve means between said compressor and said inlet ports, means for controlling the rate of delivery of scavenging air from the compressor, and means connecting said control means and said butterfly valve means so that the delivery rate of scavenging air is reduced with closing movement of the butterfly valves and vice versa.

2. A multi-cylinder engine as claimed in claim 1 in which the means for controlling the rate of scavenging air delivery comprises an open bypass from the outlet to the inlet of said compressor, and a valve in said bypass connected with said butterfly valve means restricting the flow in said bypass as said butterfly valve means moves in opening direction and vice versa.

3. A multi-cylinder two-stroke internal combustion engine of the spark ignition typehavinginlet and exhaust ports for each cylinder and in which a group of cylinders do not have a common scavenging period, supply conduit means individual to each group of cylinders, a compressor supplying scavenging air to said cylinders through said conduit means, butterfly valve means in each conduit means and connected together for simultaneous actuation, means for controlling the rate of delivery of scavenging air from the compressor, and means connecting said control means and said butterfly valve means so that the delivery rate of scavenging air is reduced with closing movement of the butterfly valves and vice versa.

'4. A multi-cylinder engine as claimed in claim 3 in which the means for controlling the rate of scavenging air delivery comprises, a bypass from the outlet to the inlet of said compressor, and a valve in said bypass connected with said butterfly valve means restricting the flow in said bypass as said butterfly valve means moves in opening direction and vice versa.

5. A multi-cylinder two-stroke internal combustion engine of the spark ignition type having inlet and exhaust ports for each cylinder and in which cylinders not having a common scavenging period are grouped, a supply conduit individual to each group of cylinders, a compressor supplying scavenging air to said cylinders through said conduit, connections from said supply conduit to said inlet ports, butterfly valve means in said connections connected together for simultaneous actuation, means for controlling the rate of delivery of scavenging air from the compressor, and means connecting said control means and said butterfly valve means so that the delivery rate of scavenging air is reduced with closing movement of the butterfly valves and vice versa.

6. A multi-cylinder two-stroke internal combustion engine of the spark ignition type having inlet and exhaust ports for each cylinder, supply conduit means individual to each cylinder, a centrifugal compressor supplying scavenging air, a common conduit connecting said compressor to said conduit means, butterfly valve means in each individual supply conduit means connected together for simultaneous actuation, whereby the eifective flow section may be reduced in each supply conduit means individually on reduction of rate of delivery of scavenging air through said common conduit.

References Cited in the file of this patent UNITED STATES PATENTS 1,574,130 Smith Feb. 23, 1926 1,745,020 Lawrence Jan. 28, 1930 1,967,069 Shoemaker July 17, 1934 2,067,757 Fielden Jan. 12, 1937 2,067,984 Ross Jan. 19, 1937 2,164,451 Fast July 4, 1939 2,230,740 Birkigt Feb. 4, 1 941 2,252,512 Keller Aug. 12, 1941 2,281,585 Kadenacy May 5, 1942 2,330,866 Camner Oct. 5, 1943 2,728,333 Albinson Dec. 27, 1955 

